1. Field of the Invention
The present invention relates to a planar light source device comprising optical fiber, a display device having the planar light source device, a method for manufacturing the light source device and display device, and a method for driving the display device.
2. Description of the Related Art
Together with the advancement of the multimedia era, liquid crystal display devices are rapidly becoming widely used in projector devices, mobile phones, and in other small devices, and in notebook computers, monitors, televisions, and other large devices. Among liquid crystal display devices, a backlight for illuminating the liquid crystal panel from the backside is ordinarily disposed in transmissive or semi-transmissive liquid crystal display devices.
Backlights include direct backlights and side-type backlights. Direct backlights have a cold-cathode fluorescent lamp or another light source disposed on the backside of a liquid crystal panel. Side-type backlights, on the other hand, have a light-guide plate disposed on the backside of the liquid crystal panel, and a cold-cathode fluorescent lamp or another light source disposed to the side of the light-guide plate. The light-guide plate is ordinarily a wedge-shaped plate comprising a transparent material, and light emitted from the light source enters the light-guide plate from the side surface of the base portion in which the plate thickness is relatively thick. In the course of light propagating toward the distal end in which the plate thickness is relatively thin, planar light is emitted from the surface thereof (see patent reference 1 (Japanese Laid-open Patent Application No. 2000-194273), for example).
Backlights that use optical fiber have also recently been developed. Backlights in which optical fiber is used have a high light utilization efficiency with minimal optical loss in comparison with backlights that use a light-guide plate, and are fundamentally advantageous in that the light-emitting state can be varied for each scan line by mutually varying the light that enters the optical fibers.
FIG. 1 is a perspective view showing the liquid crystal display device described in patent document 2 (Japanese Laid-open Patent Application No. 8-221005). A liquid crystal panel 502 is disposed in the conventional liquid crystal display device 501, and a backlight 503 is disposed on the backside of the liquid crystal panel 502, as shown in FIG. 1. Disposed in the backlight 503 are a light source 504 and a bundle 506 of optical fibers 505 optically coupled to the light source 504. The bundle 506 is an arrangement of numerous mutually parallel optical fibers 505 that are fixed in place by an adhesive to form a rectangular parallelepiped block that is diagonally cut. The section of the block forms a light-emitting surface 507 and the light-emitting surface 507 faces the reverse side of the liquid crystal panel 502.
However, there are a number of problems in the liquid crystal display device disclosed in Japanese Laid-open Patent Application No. 2000-194273. In the liquid crystal display device depicted in FIG. 1, numerous optical fibers 505 must be used to form a bundle in order to illuminate the entire display area of the liquid crystal panel 502 with light emitted from the end portions of the optical fibers 505. As a result, the thickness and the mass of the backlight increase. It is also difficult to optically couple numerous optical fibers 505 to a single light source 503, and the layout of the coupling unit is bulky and the light utilization efficiency is reduced.
In view of the above, patent document 3 (Japanese Patent No. 3008919) discloses a technique whereby notches are formed at intermediate locations in the optical fibers, and light is emitted from the notches. Optical fibers arrayed in a single row can thereby illuminate an entire display area. FIG. 2 is a diagram showing the backlight described in Japanese Patent No. 3008919. Optical fibers 512 are arrayed in a single row on the backside of a liquid crystal panel (not shown) in the conventional backlight 511, and the end portions of the optical fibers 512 are optically coupled to each of the light sources 513a, 513b, and 513c, as shown in FIG. 2. The light sources 513a, 513b, and 513c emit red (R), green (G), and blue (B) light, respectively. A plurality of notches (not shown) is formed on the side surface of the optical fibers 512. Light emitted from the light sources 513a, 513b, and 513c enters the optical fibers 512 from the end portions of the optical fibers 512, and the light is emitted from the notches in the optical fibers 512 toward the liquid crystal panel. In the backlight 511, since the optical fibers can be arranged in a single row in comparison with the backlight 503 shown in FIG. 1, the number of optical fibers can be reduced. The backlight can thereby be made lighter and thinner.
However, the above-described prior art has the following problems. It is difficult to optically couple each of the light sources 513a, 513b, and 513c to all of the optical fibers 512 in the backlight shown in FIG. 2. In other words, since the layout is bulky, the area required for the layout is greater, positioning between the light sources and the optical fibers is difficult, the precision of the positioning is poor, and the light utilization efficiency is reduced.